Commit2 JT 051519

[Syntax:]

pair_style lj/cut/dipole/cut cutoff (cutoff2)

pair_style lj/sf/dipole/sf cutoff (cutoff2)

pair_style lj/cut/dipole/long cutoff (cutoff2)

pair_style lj/long/dipole/long flag_lj flag_coul cutoff (cutoff2) :pre

cutoff = global cutoff LJ (and Coulombic if only 1 arg) (distance units) :ulb,l

cutoff2 = global cutoff for Coulombic and dipole (optional) (distance units) :l

flag_lj = {long} or {cut} or {off} :l

  {long} = use long-range damping on dispersion 1/r^6 term

  {cut} = use a cutoff on dispersion 1/r^6 term

  {off} = omit disperion 1/r^6 term entirely :pre

flag_coul = {long} or {off} :l

  {long} = use long-range damping on Coulombic 1/r and point-dipole terms

  {off} = omit Coulombic and point-dipole terms entirely :pre

pair_style spin/dipole/cut cutoff 

pair_style spin/dipole/long cutoff

pair_style spin/dipole/long/qsymp cutoff :pre

cutoff = global cutoff for Magnetic dipole energy and forces

(optional) (distance units) :ulb,l

:ule

[Examples:]

pair_style lj/cut/dipole/cut 10.0

pair_coeff * * 1.0 1.0

pair_coeff 2 3 1.0 1.0 2.5 4.0 :pre

pair_style spin/dipole/cut 10.0

pair_coeff * * 10.0 

pair_coeff 2 3 8.0 :pre

pair_style lj/sf/dipole/sf 9.0

pair_style spin/dipole/long 9.0

pair_coeff * * 1.0 1.0

pair_coeff 2 3 1.0 1.0 2.5 4.0 scale 0.5

pair_coeff 2 3 1.0 1.0 2.5 4.0 :pre

pair_style lj/cut/dipole/long 10.0

pair_coeff * * 1.0 1.0

pair_coeff 2 3 1.0 1.0 2.5 4.0 :pre

pair_style lj/long/dipole/long long long 3.5 10.0

pair_style spin/dipole/long/qsymp 10.0

pair_coeff * * 1.0 1.0

pair_coeff 2 3 1.0 1.0 2.5 4.0 :pre

[Description:]

Style {lj/cut/dipole/cut} computes interactions between pairs of particles

that each have a charge and/or a point dipole moment.  In addition to

the usual Lennard-Jones interaction between the particles (Elj) the

charge-charge (Eqq), charge-dipole (Eqp), and dipole-dipole (Epp)

interactions are computed by these formulas for the energy (E), force

Style {spin/dipole/cut} computes a short-range dipole-dipole

interactions between pairs of magnetic particles that each 

have a magnetic spin. 

The magnetic dipole-dipole interactions are computed by the

following formulas for the energy (E), force

(F), and torque (T) between particles I and J.

:c,image(Eqs/pair_dipole.jpg)

2.4824 0.01948336

2.8665 0.01109

4.0538 -0.0002176

4.753 -0.001714

4.965 -0.001986

#Program fitting the exchange interaction

#Model curve: Bethe-Slater function

import numpy as np, pylab, tkinter

import matplotlib.pyplot as plt

from scipy.optimize import curve_fit

from decimal import *

print("Loop begin")

#Definition of the Bethe-Slater function

def func(x,a,b,c):

    return 4*a*((x/c)**2)*(1-b*(x/c)**2)*np.exp(-(x/c)**2)

#Exchange coeff table (data to fit)

rdata, Jdata = np.loadtxt('exchange_bcc_iron.dat', usecols=(0,1), unpack=True)

plt.plot(rdata, Jdata, 'b-', label='data')

#Perform the fit

popt, pcov = curve_fit(func, rdata, Jdata, bounds=(0, [500.,5.,5.]))

plt.plot(rdata, func(rdata, *popt), 'r--', label='fit')

#Print the fitted params

print("Parameters: a={:.10} (in meV), b={:.10} (adim), c={:.10} (in Ang)".format(*popt))

#Ploting the result

plt.xlabel('r_ij')

pylab.xlim([0,6.5])

plt.ylabel('J_ij')

plt.legend()

plt.show()

print("Loop end")

            6            8

 Optimal parameter set

            1    4.100199340884814       F

            2    1.565647547483517       F

            1   0.9332056681088162       T    3.000000000000000     

            2   -1.162558782567700       T    2.866666666666670     

            3  -0.3502026949249225       T    2.733333333333330     

            4   0.4287820835430028       T    2.600000000000000     

            5    4.907925057809273       T    2.400000000000000     

            6   -5.307049068415304       T    2.300000000000000     

            1  -0.1960674387419232       F    4.100000000000000     

            2   0.3687525935422963       F    3.800000000000000     

            3   -1.505333614924853       F    3.500000000000000     

            4    4.948907078156191       T    3.200000000000000     

            5   -4.894613262753399       T    2.900000000000000     

            6    3.468897724782442       T    2.600000000000000     

            7   -1.792218099820337       T    2.400000000000000     

            8    80.22069592246987       T    2.300000000000000